An Australian jumping spider's restless nights
· BehindLines newsroom
What does a spider do when it stops hunting? For Portia fimbriata, a small Australian jumping spider, the night is more than a motionless break. Research presented on 27 October by the Leibniz institute (LIB) describes two distinct sleep phases. One involves moving eyes and twitching muscles, recalling the REM stage of sleep in vertebrates.
Watching is not enough
The researchers combined several observations to distinguish sleep from simply staying still. The University of Bonn, which leads the team, describes infrared recordings made at night and tests of responses to a sound stimulus. The animals were also observed after their sleep had been interrupted, to look for compensatory rest.
In interviews published by ABC Science on 27 October, researcher Nadja Geiger reports slower responses, especially during the REM-like phase. Some individuals did not react to the signal. These tests therefore offer more evidence than footage of moving legs alone.
A resemblance does not establish dreaming
The term REM sleep may invite us to imagine a spider's nocturnal adventures. But Bonn explains that the team did not measure brain activity: its conclusions rely on behaviour. Observing a similar phase cannot tell us what the animal experiences, or establish that it dreams.
That distinction is the main guide to interpreting the result. Movements can be observed; the possible content of a dream cannot be observed in this experiment. The work concerns this species and does not describe all spiders.
Comparing very different animals
According to the Leibniz Institute, further work will examine the diversity of these phases among spiders and their possible links with cognitive abilities. For readers, the interest lies in an open question: how far can very different nervous systems produce comparable forms of rest? The little hunter provides a setting for investigation, without supplying all the answers.